Fauna of the Morrow Group 
147 
1910. Derbya robusta. Raymond, Ann. Carnegie Mus., vol. 7, p. 158, pi. 
27, fig. 8. 
Ames limestone: Glenwood, Pennsylvania. 
1911. Derbya robusta. Raymond, Penn. Topog. and Geol. Surv. Comm., 
Rep. for 1908-10, pi. 6, fig. 8. 
Ames limestone: Glenwood, Pennsylvania. 
Two pedicle valves and a number of brachial valves of this 
species are in the Morrow collections. They vary in length from 
less than 15 mm. to more than 45 mm. and display varying 
convexities depending upon the age of the individual. The 
surface markings when well preserved consist of radiating striae 
crossed by concentric growth lines, the latter more closely spaced 
and much finer than the former. One of the pedicle valves 
shows the high cardinal area, the vertically elongated delthyrium 
closed by the convex deltidium, and the median septum typical 
of the species. 
Horizon and locality. Hale formation : East Mountain, Fay- 
ville, Arkansas (Stations 136, 137, and 149) ; Brentwood 
limestone: vicinity of Fayetteville, Arkansas (Stations 134, 135, 
and 153). Kessler limestone: near Brentwood (Station 144), 
and on East Mountain, Fayetteville (Station 209), Arkansas. 
Morrow formation: near Choteau, Oklahoma (Station 306). 
Orthotetes? sp. 
Plate IX, figure 8. 
A number of brachial valves of a strophomenoid brachiopod 
from the Brentwood limestone represents a form that is prob- 
ably an undescribed species of Orthotetes. The shell is large, 
transversely elongated, with the hinge-line greater than any 
other diameter; it is rendered distinctly bilobate by an unde- 
fined rounded mesial sinus. The surface ornamentations con- 
sist of bifurcating, radiating striae crossed by fine concentric 
lines of growth. A nearly perfect example has a width along 
the hinge-line of 46 mm. and a length of 21 mm. In the absence 
of the pedicle valve it is impossible to identify the form generic- 
ally with any degree of confidence. 
Horizon and locality. Brentwood limestone: near Fayette- 
ville, Arkansas (Station 135) ; Sawney Hollow, Oklahoma (Sta- 
tion 210). 
